suggested that the phenomena may be accounted
for far more naturally, by supposing that lava flowing simultaneously
from the different orifices, and principally from Jorullo, united into a
sort of pool or lake. As they were poured forth on a surface previously
flat, they would, if their liquidity was not very great, remain thickest
and deepest near their source, and diminish in bulk from thence towards
the limits of the space which they covered. Fresh supplies were probably
emitted successively during the course of an eruption which lasted more
than half a year; and some of these, resting on those first emitted,
might only spread to a small distance from the foot of the cone, where
they would necessarily accumulate to a great height. The average slope
of the great dome-shaped volcanoes of the Sandwich Islands, formed
almost exclusively of lava, with scarce any scoriae, is between 6
degrees 30 minutes and 7 degrees 46 minutes, so that the inclination of
the convex mass around Jorullo, if we adopt Mr. Scrope's explanation
(see fig. 57), is quite in accordance with the known laws which govern
the flow of lava.

The showers, also, of loose and pulverulent matter from the six craters,
and principally from Jorullo, would be composed of heavier and more
bulky particles near the cones, and would raise the ground at their
base, where, mixing with rain, they might have given rise to the stratum
of black clay, which is described as covering the lava. The small
conical mounds (called "hornitos," or little ovens) may resemble those
five or six small hillocks which existed in 1823 on the Vesuvian lava,
and sent forth columns of vapor, having been produced by the
disengagement of elastic fluids heaping up small dome-shaped masses of
lava. The fissures mentioned by Humboldt as of frequent occurrence, are
such as might naturally accompany the consolidation of a thick bed of
lava, contracting as it congeals; and the disappearance of rivers is the
usual result of the occupation of the lower part of a valley or plain by
lava, of which there are many beautiful examples in the old
lava-currents of Auvergne. The heat of the "hornitos" is stated to have
diminished from the first; and Mr. Bullock, who visited the spot many
years after Humboldt, found the temperature of the hot spring very
low,--a fact which seems clearly to indicate the gradual congelation of
a subjacent bed of lava, which from its immense thickness may have been
enabled to ret